US Patent 7969895 Switch apparatus and network system

A switch apparatus providing with a loop detection function sets a port identification to a port which activates the loop detection function, only receives the loop detection frame by a high-order port in the switch apparatus connected with a backbone network or a high-order switch apparatus on the basis of the port identification set previously, and controls an inactivation of a sending source low-order port that sent the loop detection frame, when the loop detection frame is received by the high-order port.